1. Field of the Invention
The present invention relates generally to ink jet printers and more particularly, the invention pertains to star wheels, and a manufacturing process for star wheels provided as part of the media transport path in for a high speed ink jet printer.
2. Description of the Related Art
Ink jet printers are used commonly in offices and home printing applications. Ink jet printers are popular due to their low cost of operation, low energy use and quiet operating features. Ink jet printing involves ejection of tiny ink droplets through small holes, in a controlled manner, to create the desired image. Ink is supplied from an ink reservoir to a printing head, which includes various passageways from the reservoir to the nozzle orifices. Energy is applied to the ink from an ink droplet generator near each orifice, which may include the application of electrostatic attraction, the application of oscillating forces from piezo elements, the application of heat from heating elements, or the like.
Controlling the media in the print zone is critical, in order to provide proper positioning of the print media for the reception of ink droplets applied by the printhead. It is known to use star wheels opposite exit drive wheels in opposed roll couples, to prevent media from buckling in or around the print zone. As implied by their name, star wheels have a plurality of radially extending tips on the periphery thereof, which engage the surface of a printed sheet passing between the star wheel and the opposed drive roller.
Laser printers are also used in both home and office applications. Although generally more costly than ink jet printers, laser printers are sometimes preferred for the perceived greater print quality and the faster printing speed available from laser printers.
For ink jet printers to compete more favorably with laser printers, it is necessary to increase the printing speed and the optical density of the printed image obtained from an ink jet printer. These performance increases in an ink jet printer must be achieved without increased occurrence of ink smear.
Improved ink formulations have been developed, and incorporate binders and flocculants to eliminate smear and provide an optical density for the printed image approaching that available with laser printers. While quick dry times are available, increased printing speeds in ink jet printers can result in still wet ink being present as the sheet exits the printer. Ink may be transferred to the tips of the star wheels, as the star wheel tracks over the printed surface. Paper dust and fibers can accumulate, together with the ink, into a mass on the star wheel tip. A mechanical lock occurs between the star wheel surface and the mixture of ink, dust and fiber. The accumulation at the star wheel tip acts as a sponge, absorbing additional ink from wet portions of printed media passing thereunder. The absorbed ink can be re-deposited on non-printed areas of the sheet contacted by the accumulation at the star wheel tip. Print quality is degraded not so much by the removal of ink from the printed area, but by the redeposit of ink on the unprinted areas of the media.
It is necessary to make the star wheel from material of sufficient resistance to withstand the abrasion from paper over time. Selecting material of initially lower surface resistance can reduce the propensity for ink to adhere to the wheel, and the subsequent mechanical lock between the star wheel surface and the accumulation of ink, fiber and dust. However, such materials generally are prone to wear more rapidly, creating surface roughness and an increasing propensity for ink to adhere to the star wheel. Coating star wheels formed by chemical etching is unsatisfactory in that the coating deposition is not uniform on the relatively rough surface of a chemically etched star wheel. Manufacturing techniques other than chemical etching can be used to yield better surface finishes; however, the increased manufacturing cost makes the use of these techniques undesirable.
What is needed in the art is a star wheel, and a manufacturing process for making a star wheel, which can withstand the abrasion created by contact with paper over time, yet which has a smooth finish reducing the tendency for ink to adhere to the star wheel tip surface.
The present invention provides a manufacturing process for making star wheels suitable for ink jet printers, which yields star wheels having improved surface smoothness, with the optional application of coatings having consistent thickness.
The invention comprises, in one form thereof, a method for forming a printer star wheel. The method includes steps of providing metal to be used in the star wheel; forming the metal into the desired star wheel shape; and electropolishing at least a portion of the star wheel.
The invention comprises, in another form thereof, a star wheel having a metallic body; a plurality of radially extending projections having tips; and at least a portion of the tips having an electropolished surface.
The invention comprises, in yet another form thereof, an ink jet printer having a print station and a paper transport path therethrough. The paper transport path includes a star wheel for engaging printed surfaces of media exiting the print station. The star wheel has a plurality of projections, and an electropolished surface on the projections.
An advantage of the present invention is that known, acceptable material can be used for manufacturing a star wheel, and treated with an economically advantageous process to reduce the propensity for ink, fiber and dust to adhere to the star wheel.
Another advantage of the present invention is providing a star wheel for an ink jet printer which is resistant to wear from long-term contact with paper, and which resists the accumulation of ink at the star wheel tips even after prolonged contact with wet ink on printed media surfaces.
Yet another advantage of the present invention is providing a high-speed ink jet printer having reduced ink tracking from star wheel contact with the printed surface of freshly printed media.
Still another advantage of the present invention is providing a process for applying a smooth, consistent coating to a metal object, such as a printer star wheel, and providing a printer star wheel having a coating of acceptable thickness consistency.
A further advantage of the present invention is providing a star wheel structure in which any accumulation of ink, dust and fiber tends to occur away from the tips of the star wheel, and away from the portions of the star wheel which come into contact with media passing thereunder.